pooling

Pooling Drives

• Linux Solutions
• Windows Solutions

Linux

There are two main ways to pool drives in Linux that are favorable to using SnapRAID. The first is AUFS (Another Unified File System) and the second and probably better choice is mhddfs (Multi Hard Disk Device File System). Both are FUSE (Filesystem in Userspace) which typically means slower. However, as computers get faster and faster, the limitations with FUSE have gone away. The idea is that the file system interacts with the user space layer, then the hardware layer and then from the hardware layer into the user space layer, adding a step both ways on each operation causing a massive slow down. Again, on decent hardware such as a Xeon E3-1220V3 with 8+ GB of ECC ram, this isn't going to bottleneck the process. Now if you are using this on a Raspery Pi, then you've made a poor choice in your NAS (Network Attached System).

MHDDFS - This used to be the poorer choice due to not being compiled into the kernel. However it became the better choice when AUFS was removed from the kernel. MHDDFS is very simple. Unlike AUFS which has file allocation abilities such as round robin, and most free space, MHDDFS only uses most free space. Meaning that files will be placed onto the drive with the most free space. This typically works well for SnapRAID as it keeps the parity file about even with the drives. Meaning a full drive doesn't cause the parity files to become too big for their own drive.

To setup mhddfs, you must first download it. sudo apt-get install mhddfs

Then mount the drives you want to pool to mount points. This works well since SnapRAID can use the same mount points for making the parity files. We're going to assume that sda, sdb, and sdc are three drives in the computer.

sudo mkdir A00,A01,A02,pool sudo mount /dev/sda1 A00 sudo mount /dev/sdb1 A01 sudo mount /dev/sdc1 A02 mhddfs mhddfs A00,A01,A02 Pool -o allow_other

That is a mhddfs pool in the most basic of the sense. The directory pool will have the contents of the three drives merged in its mount point. If the same file exists on two or more drives, the newest one is the one you will see. Deleting that file will delete both files. A simple pool.

AUFS - This used to be the better solution, however as of Linux Kernel 3.6, this is no longer compiled into the kernel turning it into a FUSE based system. AUFS has an issue where it creates whiteout files when it can't lock a file for deletion. For some reason or another, these files never get deleted. Compounding this problem is that a poorly formed whiteout file can make a drive look empty but still use all the space as all the files are still there, only hidden by AUFS. As such, the following examples are just that, examples and should not be used on kernels at or above 3.6.

Lets download it first apt-get install aufs-tools

sudo mkdir A00,A01,A02,pool sudo mount /dev/sda1 A00 sudo mount /dev/sdb1 A01 sudo mount /dev/sdc1 A02 mount -t aufs -o br=A00=rw:A01=rw:A02=rw -o create=mfs none pool

AUFS gives you a little more control, such as Read Write and Read Only permissions. However, the whiteout files are a serious hindrance that will eventually creep up. It is advisable to stick with MHDDFS.

Windows

There are two major choices, nether is free. There are two free choices, but they are unwieldy and not for every day use.

PAID FOR Driveblender - Unknown

Stablebit Drive Pool - DP is a basic front end and a .NET program that puts drives together while also adding in file duplication for added safety. If using SnapRAID , this safety isn't really needed. Turn it off in the settings. You'll need to use Disk Management to make a set of drive mount points. Then make sure hidden files and folders it ticked off under folder options. On each drive there will be a hidden folder with a large array of letters and numbers. This is the DP GUID. Setting this up is more complicated than Linux and will require some cliking and config work.

SnapRAID Pooling - Unknown

Liquesce - http://liquesce.codeplex.com/ Status Unknown